1. Field of the Invention
The present invention relates to a thin film magnetic head in general employed in a magnetic recording medium drive such as a magnetic disk drive, including a hard disk drive (HDD), and a magnetic tape drive.
2. Description of the Prior Art
A thin film magnetic head in general comprises a central magnetic core disposed within a thin film coil spreading over a plane. An upper and a lower magnetic pole layer are designed to extend forward from the central magnetic core, respectively, toward a medium-opposed surface of a head slider. The head slider is designed to be opposed to a recording disk at the medium-opposed surface such as a bottom surface, including an air bearing surface, for example. The gap layer is interposed between the upper and lower magnetic pole layers.
The tip or front end of the upper magnetic pole layer is received at a narrower upper front magnetic pole piece exposing its tip or front end at the medium-opposed surface, as is disclosed in Japanese Patent Application Laid-open No. 7-225917, for example. The upper front magnetic pole piece is opposed to the front end of a narrower lower magnetic pole piece across the gap layer. The lower front magnetic pole piece is connected to the front end of the lower magnetic pole layer.
The disclosed thin film magnetic head is designed to allow magnetic flux, generated in the thin film coil, to be transmitted to the upper front magnetic pole piece through the upper magnetic pole layer. If the upper front magnetic pole piece is designed to contact the upper magnetic pole layer over a larger contact area, saturation of the magnetic flux can be suppressed at the contact area, so that a larger or stronger magnetic field for recordation can be obtained at the gap between the upper and lower front magnetic pole pieces along the medium-opposed surface. Accordingly, the upper front magnetic pole piece is required to extend rearward from the medium-opposed surface by a larger longitudinal length in the back-and-forth direction.
In recent years, a so-called core width of the upper and lower front magnetic pole pieces gets remarkably smaller or narrower than that of the upper magnetic pole layer, as is apparent from the aforementioned Japanese Patent Application Laid-open No. 7-225917. The core width can be measured along the medium-opposed surface in the lateral direction of a recording track. The narrower core width inevitably induces reduction in the magnetic field for recordation at the gap between the upper and lower front magnetic pole pieces along the medium-opposed surface.
Japanese Patent Application Laid-open No. 6-314414 discloses a proposal to maintain a stronger magnetic field for recordation at the gap between the upper and lower front magnetic pole pieces along the medium-opposed surface. The proposal employs a swelling with a backward step formed on the lower front magnetic pole piece at a location spaced from the medium-opposed surface. Such a swelling serves to concentrate the magnetic flux at the front ends of the upper and lower front magnetic pieces. A stronger magnetic field may leak out of the medium-opposed surface at the gap.
However, it is difficult to form or shape the swelling on the lower front magnetic pole piece of a narrower width and smaller dimensions. Even if the swelling can be formed, it is much difficult to align the narrower upper front magnetic pole piece with such a narrower swelling with the gap layer interposed therebetween.
It is accordingly an object of the present invention to provide a thin film magnetic head capable of aligning an upper front magnetic pole piece with a lower front magnetic pole piece without any difficulty even when the lower front magnetic pole piece is reduced in the longitudinal direction as compared with the upper front magnetic pole piece.
According to the present invention, there is provided a thin film magnetic head comprising: a thin film coil; a central magnetic core disposed within the thin film coil; an upper magnetic pole layer extending forward from the central magnetic core above a datum plane; a lower magnetic pole layer extending forward from the central magnetic core below the datum plane; an upper front magnetic pole piece receiving a front end of the upper magnetic pole layer and extending rearward over the datum plane from its front end exposed at a medium-opposed surface; and a lower front magnetic pole piece connected to a front end of the lower magnetic pole layer and extending below the datum plane in a lateral direction along the medium-opposed surface by a lateral width larger than that of the upper front magnetic pole piece, wherein the lower front magnetic pole piece extends rearward from the medium-opposed surface by a longitudinal length smaller than that of the upper front magnetic pole piece.
With the above arrangement, a magnetic flux generated in the central magnetic core within the thin film coil circulates through the upper and lower magnetic pole layers. In particular, the magnetic flux tends to run through the upper front magnetic pole piece of a first longitudinal length to the lower front magnetic pole piece of a second longitudinal length smaller than the first longitudinal length. The lower front magnetic pole piece serves to concentrate the magnetic flux at the front ends of the upper and lower front magnetic pole pieces. Accordingly, a larger or stronger magnetic field for recordation can be obtained along the medium-opposed surface of a head slider.
In addition, the lower front magnetic pole piece is designed to have a larger lateral width in the lateral direction irrespective of a smaller length in the longitudinal direction as described above. As compared with the case where the lower front magnetic pole piece is designed to have a narrower width corresponding to that of the upper front magnetic pole piece, the production of the lower front magnetic pole piece can remarkably be facilitated. Moreover, a larger width of the lower front magnetic pole piece in the lateral direction serves to facilitate alignment of the upper front magnetic pole piece with the lower front magnetic pole piece in the lateral direction.
The lower front magnetic pole piece is preferably designed to have a saturation flux density larger than that of the lower magnetic pole layer. The set saturation flux density contributes to reliable avoidance of saturation of flux in the lower front magnetic pole piece. In the case where 80Ni20Fe is employed in the lower magnetic pole layer for achieving Bs=1.0T, 50Ni50Fe or 45Ni55Fe can be employed for the lower front magnetic pole piece. 50Ni50Fe usually achieves Bs=1.4T, and 45Ni55Fe is usually employed to achieve Bs=1.6T.
The upper magnetic pole layer may retract its front end from the medium-opposed surface. The retracted upper magnetic pole layer serves to avoid undesirable leakage of magnetic flux which interferes with the magnetic field for recordation at the medium-opposed surface. In this case, if the lower front magnetic pole piece has the longitudinal length smaller than that of the upper front magnetic pole piece, the retracted upper magnetic pole layer fails to reduce or weaken the magnetic field for recordation. A conventional retracted upper magnetic pole layer tends to induce reduction in the magnitude of the magnetic field for recordation.
The lower front magnetic pole piece may be provided with a protrusion formed on an upper surface of the lower front magnetic pole piece so as to have a lateral width corresponding to that of the upper front magnetic pole piece. The protrusion is thus allowed to keep the aforementioned second longitudinal length while a narrower gap can be defined between the protrusion and the upper front magnetic pole piece. Accordingly, the width of a recording track on the recording medium can further be reduced, keeping a stronger or larger magnetic field for recordation.
Alternatively, the lower front magnetic pole piece may be provided with a longitudinal protrusion formed on an upper surface of the lower front magnetic pole piece so as to extend rearward from the medium-opposed surface by a third longitudinal length smaller than the second longitudinal length of the lower front magnetic pole piece. The longitudinal protrusion is designed to have a lateral width corresponding to that of the upper front magnetic pole piece. In this case, a lateral protrusion is preferably connected to the rear end of the longitudinal protrusion so as to extend on the upper surface of the lower front magnetic pole piece by the lateral width larger than that of the longitudinal protrusion.
The lateral protrusion serves to define a front wall surface standing from the lower front magnetic pole piece at a position retracted from the medium-opposed surface. The front wall surface defines, in addition to a first edge extending along the medium-opposed surface in the lateral direction from the front end of the longitudinal protrusion, a second edge extending in the lateral direction from the rear end of the longitudinal protrusion. In this type of the thin film magnetic head, the magnetic flux introduced into the lower front magnetic pole piece is allowed to run toward the upper front magnetic pole piece out of the first and second edges, respectively. The separation or divergence of the magnetic flux in this manner serves to reliably reduce or suppress the leakage of a magnetic field out of the medium-opposed surface from the lower front magnetic pole piece. The reduction or suppression in the leakage of the magnetic field is expected to contribute to a further reduction in the width of a recording track.
The aforementioned thin film magnetic head can be employed in a recording medium drive such as a magnetic disk drive, including a hard disk drive (HDD), and a magnetic tape drive.